Fix: import field from dataclasses for PullReqMeta

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

third_party/vllm/vllm/distributed/kv_transfer/kv_connector/v1/mooncake/mooncake_connector.py

@@ -5,7 +5,7 @@ import threading
 import time
 from collections import defaultdict
 from concurrent.futures import ThreadPoolExecutor
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from enum import IntEnum
 from typing import TYPE_CHECKING, Any